(a) Field of the Invention
The present invention relates to a charger of a low voltage battery and a method thereof. More particularly, the present invention relates to a charger of a low voltage battery and a method thereof that can control a charge voltage of the low voltage battery based on an air amount supplied to the fuel cell, and improve fuel consumption and durability of the fuel cell.
(b) Description of the Related Art
A fuel cell system that is applied to a hydrogen fuel cell vehicle, a type of environment-friendly vehicle, includes a fuel cell stack that generates electrical energy with an electrochemical reaction of a reaction gas, a hydrogen supply device that supplies hydrogen, which is a fuel, to the fuel cell stack, an air supply device that supplies air including oxygen, which is an oxidizing agent necessary for an electrochemical reaction, to the fuel cell stack, a heat and water management system that optimally adjusts an operation temperature of the fuel cell stack by discharging heat, which is a by-product of an electrochemical reaction of the fuel cell stack, to the exterior and that performs a water management function, and a fuel cell system controller that operates the fuel cell system.
In a vehicle in which such a fuel cell system is mounted, when using a fuel cell as a power source, the fuel cell is responsible for the loads of constituent elements of the vehicle, and thus in an operating area in which efficiency of the fuel cell is low, performance may deteriorate. Further, when a sudden load is applied to the vehicle, power may not be fully supplied to a driving motor and thus performance of the vehicle may deteriorate due to the generation of electricity by a chemical reaction causing a sudden load change to the fuel cell.
Further, since the fuel cell has one direction output characteristics, when no separate power storage is present and the vehicle brakes, energy that flows from a driving motor may not be recovered and thus efficiency of a vehicle system may deteriorate. Therefore, as a method of overcoming the drawbacks, a fuel cell hybrid vehicle has been developed. The fuel cell hybrid vehicle is a system that mounts a power storage, for example, a super capacitor or a high voltage battery as a separate auxiliary power source for providing power necessary for driving a load, such as a driving motor in addition to a fuel cell, which is a major power source in a vehicle.
In a fuel cell-battery hybrid vehicle, a fuel cell that is used as a major power source and a high voltage battery that is used as an auxiliary power source may be coupled in parallel, and the high voltage battery (e.g., a main battery) and a low voltage battery (e.g., a 12 V auxiliary battery) for driving low voltage driving components of the vehicle are mounted, i.e., a high voltage battery and a low voltage battery, which are two types of batteries, may be mounted together.
Meanwhile, the fuel cell is configured to generate electrical energy by reaction of hydrogen and oxygen, and the electrical energy amount generated at the fuel cell stack is proportional to hydrogen amount supplied to the fuel cell stack. The hydrogen amount supplied to the fuel cell stack is determined based on an air amount supplied to the fuel cell stack. Therefore, techniques for minimizing hydrogen used in the fuel cell stack and improving fuel consumption by varying a charge voltage of the low voltage battery that charges electrical energy generated at the fuel cell stack are required.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.